1. Field of the Invention
The present invention relates to a process for producing dicarboxylic acids that are useful as, for example, raw materials for polyamides and polyesters, and intermediate materials for fine chemicals. More specifically, it relates to a process of oxidative cleavage of a cycloalkane with oxygen in the presence of a catalyst to thereby yield a corresponding dicarboxylic acid.
2. Description of the Related Art
Certain processes of oxidatively cleaving a cycloalkane and/or a cycloalkanol are known as processes for producing dicarboxylic acids. For example, adipic acid, a raw material for polyamides, is produced by a process of oxidizing cyclohexanol alone or a mixture of cyclohexanol and cyclohexane with nitric acid. However, this process requires expensive facilities for exhaust gas for disposal of nitrogen oxides by-produced in the reaction.
To avoid these problems, certain processes of oxidatively cleaving a cycloalkane with molecular oxygen in the presence of an oxidation catalyst to thereby yield a corresponding dicarboxylic acid have been proposed. For example, Japanese Unexamined Patent Application Publications No. 08-38909, No. 09-327626, and No. 10-286467 each disclose a process of oxidatively cleaving a cycloalkane with oxygen in the presence of a catalyst comprising an imide compound having an N-hydroxy or N-oxo cyclic imide skeleton and a metallic compound to thereby yield a corresponding dicarboxylic acid. However, examples disclosed in these publications use a relatively large amount of the catalyst and do not always achieve sufficiently satisfactory results in their space time yields (STYs). A demand has therefore been made on a process for producing a dicarboxylic acid, which process can reduce the amount of a catalyst, can significantly improve the space time yield and can produce the dicarboxylic acid more efficiently.